Proteolytic processing is an essential component of normal cell growth, differentiation, remodeling, and homeostasis. The cleavage of peptide bonds within cells is necessary for the maturation of precursor proteins to their active form, the removal of signal sequences from targeted proteins, the degradation of incorrectly folded proteins, and the controlled turnover of peptides within the cell. Proteases participate in apoptosis, antigen presentation, inflammation, tissue remodeling during embryonic development, wound healing, and normal growth. They are necessary components of bacterial, parasitic, and viral invasion and replication within a host. Four principal categories of mammalian proteases have been identified based on active site structure, mechanism of action, and overall three-dimensional structure. (Beynon, R. J. and Bond, J. S. (1994) Proteolytic Enzymes: A Practical Approach, Oxford University Press, New York, N.Y., pp. 1-5.)
The serine proteases (SPs) are a large family of proteolytic enzymes that include the digestive enzymes, trypsin and chymotrypsin; components of the complement cascade and of the blood-clotting cascade; and enzymes that control the degradation and turnover of macromolecules of the extracellular matrix. SPs are so named because of the presence of a serine residue found in the active catalytic site for protein cleavage. The active site of all SP is composed of a triad of residues including the aforementioned serine, an aspartate, and a histidine residue. SPs have a wide range of substrate specificities and can be subdivided into subfamilies on the basis of these specificities. The main sub-families are trypases which cleave after arginine or lysine; aspases which cleave after aspartate; chymases which cleave after phenylalanine or leucine; metases which cleavage after methionine; and serases which cleave after serine.
The plasma inter-.alpha.-trypsin inhibitor family molecules are serine protease inhibitors (serpins) composed of a 240 kDa plasma protein complex of at least five different types of glycoproteins. These glycoproteins consist of four heavy (H) chains and one 30 kDa light (L) chain named H1, H2, H3, H4, and L, and are independently synthesized and proteolytically processed from precursor proteins. (Daveau, M. et al. (1998) Arch. Biochem. Biophys. 350:315-323; and Salier, J. P. et al. (1992) Mamm. Genome 2:233-239.) The plasma inter-.alpha.-trypsin inhibitor light chains have sequence similarity to the Kunitz trypsin inhibitors which appear to be present in all vertebrates. (Salier, J. P. (1990) Trends Biochem. Sci. 15:435-439.) Some examples of the Kunitz trypsin inhibitors are tissue factor pathway inhibitor, which regulates tissue factor-induced coagulation, and protease nexin-2, which regulates serum coagulation factor XIa. (Broze, G. J. (1995) Annu. Rev. Med. 46:103-112; and Wagner, S. L. et al. (1993) Brain Res. 626:90-98.) The heavy chain precursors encode a signal peptide sequence and the mature chain. Other plasma inter-.alpha.-trypsin inhibitor heavy chains have been described in human and rodents. (Bourguignon, J. et al. (1993) Eur. J. Biochem.212:771-776; Salier, 1992, supra; and Salier, J. P. (1996) Biochem. J. 315:1-9.) Proteases and protease inhibitory molecules may contain amino acid sequence motifs which determine protein-protein interactions, such as the potential metal-binding site of von Willebrand factor type A3 (vWFA3) motif, glycine-amino acid-serine-amino acid-serine. This motif is also required for ligand interaction in the homologous I-type domains of integrins CR3 and LFA-1. (Huizinga, E. G. (1997) Structure 5:1147-1156.)
The expression of the rat plasma inter-.alpha.-trypsin inhibitor genes is regulated by inflammation in vivo. The genes are predominantly expressed in the rat liver, but H2 and H3 mRNA is also present in brain, intestine, and stomach. (Daveau, supra.)
Protease inhibitors play a major role in the regulation of the activity and effect of proteases. They have been shown to control pathogenesis in animal models of proteolytic disorders and in the treatment of HIV. (Murphy, G. (1991) Agents Actions Suppl. 35:69-76; and Pakyz, A. and Isreal, D. (1997) J. Am. Pharm. Assoc. (Wash.) NS37:543-551.)
The discovery of a new growth-associated protease inhibitor heavy chain precursor and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, treatment, and prevention of reproductive, developmental, neoplastic, and immunological disorders.